Turbomachinery high speed modal balancing: Modeling and testing of scale rotors

The object of this work is the application of a modal balancing approach to turbomachinery rotors. The investigation was carried out on a small commercial rotor dynamic test bench suitably modified to represent in scale a typical turbomachinery balancing problem. Software based on literature theoretical formulations was developed for both the more widespread influence coefficient method and modal balancing. The modal balancing software was coupled with a finite element rotor dynamic code in order to determine the modal shapes necessary to impose the orthogonality conditions and calculate the modal calibration sets. Results of the two approaches were compared both in terms of balancing quality and in terms of time to balance the rotor. The test results highlighted essential information for an eventual true scale industrial application of the modal method and also interesting new aspects such as the possibility of balancing modes out of the operating speed range.